1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to a target object; and, in particular, to an active type rangefinder apparatus used in a camera or the like.
2. Related Background Art
Conventionally known as an active type rangefinder apparatus used in a camera or the like is one having light-detecting means for detecting light reflected from a target object and outputting near-side and far-side signals corresponding to the distance to the target object, comparing the far-side signal with a preset clamp signal in terms of magnitude, calculating an output ratio signal from the ratio between the greater signal determined by the comparison and the near-side signal, and converting the output ratio signal into a distance signal according to a converting expression varying depending on the value of output ratio signal as disclosed in Japanese Patent Application Laid-Open No. HEI 10-274524.
This rangefinder apparatus is aimed at obtaining rangefinding results on a par with those of a conventional system using both the light quantity and rangefinding in a short period of time without enhancing its circuit scale, so as to determine the distance to the target object uniquely and stably even when the distance is long.
Meanwhile, an operation of a signal processing IC for processing the output ratio signal and the like in this rangefinder apparatus is controlled in response to a control signal from a CPU. If noise is generated in this control signal, then the signal processing IC will not operate normally. Therefore, a plurality of control signals are fed into the signal processing IC, so as to prevent the latter from malfunctioning.
In this case, however, it is necessary to provide the signal processing IC with a plurality of input terminals for receiving the respective control signals. Installing such a plurality of input terminals inhibits reducing the cost of the signal processing IC. For cutting down the cost, it is desirable that the number of input terminals be smaller. In order for a single control signal to control an operation of the signal processing IC, it is necessary that, if an abnormality occurs in the operation due to noise or the like, then this abnormality be detected promptly.
In order to overcome such technical problems, it is an object of the present invention to provide a rangefinder apparatus which can promptly detect abnormalities in operations of its signal processing IC.
For achieving such an object, the present invention provides a rangefinder apparatus comprising light-projecting means for projecting a light beam toward a target object a plurality of times; light-receiving means for receiving reflected light of the light beam projected to the target object and outputting an output signal corresponding to a distance to the target object; signal processing means for charging or discharging an integrating capacitor according to the output signal of the light-receiving means and outputting an integrated signal according to a voltage value of the integrating capacitor; detecting means for detecting the voltage value of the integrating capacitor in a rangefinding routine; and forcible terminating means for terminating the rangefinding routine when the voltage value of the integrating capacitor is out of a preset range.
The rangefinder apparatus in accordance with the present invention may be configured such that, if it is determined that the voltage value of the integrating capacitor is out of the preset range, then the forcible terminating means repeats the rangefinding routine, and terminates the rangefinding routine if the voltage value of the integrating capacitor is also out of the preset range in thus repeated rangefinding routine.
In the rangefinder apparatus in accordance with the present invention, the signal processing means may receive a single control signal from control means and carry out signal processing thereof.
By appropriately detecting a voltage value of the integrating capacitor in a rangefinding routine, the present invention can detect whether the rangefinding routine is being carried out normally or not. As a consequence, abnormalities in operations of the rangefinder apparatus can be detected promptly.
If it is determined by detecting a voltage value of the integrating capacitor in a rangefinding routine that the rangefinding routine is not carried out normally, then the rangefinding routine can be started again, and the voltage value of integrating capacitor can be detected, so as to accurately determine whether the rangefinder apparatus is malfunctioning or not.
The present invention is effective in particular when the signal processing means carries out signal processing in response to a single control signal from control means. The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given byway of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.